Art of armor plate manufacture



`July 20, 1943.` A, L, ABBOTT 2,324,808

' v A'R'T 0Fl ARMOR PLATE MANUFAcfr'URE Y Filed Jan. 22, 1940 2 Sheets-Sheet 1 July 20,1943. A. l.. ABQTT .2,324,808

ART oF ARMOR PLATE MANUEAGTURE F11-ed Jan. 22. 1940 4 2 sheets-sheet 2 1mg/5 'AleiiLA/wl;

*WM-@ff l Patented July 20, 1943 ...L-3274.808 ,iv

OFFICE ART oF muon rmi'ra Mmm-Across Alben L. Abbott. canton. ohio, mimmto Die'- bold Safe & Lock Co corporation of Ohio mpany, Canton, Ohio, a

Application January zz, 1m, semi N9. 314,933

l(ci. 14s-.12)

l2'1 claims.

Ihe invention. relates to steel armor plate and more particularly to thin steel armor plate, such as V4", V2", and up to 1" thick steel armor plate, and to the manufacture thereof. During the last few years there has been an increasing demand for thin steel armor plate having a hard region or case at and adiacent vone or the outer surface thereof merging into a softer backing or region at and adjacent the other or inner surface thereof. i

Certain procedures for the manufacture of Athin steel armor plate have been lmown. However. there has been a recent demand -for thin armor plate for use in the constructionI of land, sea or air, offensive and defensive weapons, equipment,`

materials, and annament, having combined physical and ballistic propertieathat, so far as I have been able to determine, could not be obtained in armor plate made byknown methods.

Dimculties which characterize prior methodsl of making thin armor plate, such as V4", V2",

and up to 1" armor plate, include among others,

a resultant uneven and non-uniform hard region or case,vparticularly at and adjacentvthe plate -V edges and hole surfaces drilled prior to carburizing; an excessive loss of material which was initially provided at and adjacent the edges of plates, then processed and then-removed and scrapped, because of warpage, cracking and unevenness .of case in the regions removed; the necessity of annealing plates after carburizing. and before machining and initial sizing thereof;

the impossibility of straightening plates to remove warps, bends or buckles if the plates were fully quenched following heat treatment thereof i to develop high ballistic properties; and the impossibility of developing high ballistic properties i vention from being obtained in carrying out prior I practice.

I have discoveredl that these difficulties may be entirely eliminated and that steel armor plate of the thinner gauges, such as V4", V2, and up' to 1" armor plate, can be economically, eillcientplate has combined physical and ballistic proper ties which could notA be obtained by prior methods, and which exceed present day requirements.

It is therefore an object of the presentinvenf-v tion to provide a method of making thin steel armor plate which eliminates prior art dimcultiee and enables the production of armor plate having ballistic properties materially in excess of those obtained in thin steel armor plate manufactured in accordance with prior practice.

It is also an object of the present invention to eliminate inner surfacel carburization, to eliminate undesirable warpage, to prevent cracking, to prevent uneven edge carburization; to eliminate mined` hole surface earburizauon, and to provide i to eliminate an annealing operation following the carburizing step and-preceding machining, drilling, cutting, shearing and sizing (and bending if required), of carburized plates in a-method of making thin steel armor plate.

It is also an object of the present inventiontoj provide a method of making thinsteel armor Y plate, which enables a stock or reserve of carburized plates to be built upand drawn from at ly and speedily marie by an entirely new and.

radically different manufacturing procedure, which, with respect to prior procedures, eliminates some operations, changes the character of other operations, changes the order of many, operations, and utilizes uncontrollable diiliculties inherent in prior procedure as procedural aids or advantages; so that the resulting thin steel armor the stage of manufacture `where .machining drilling and shaping to size in accordance with specifications occurs.

It is also an object of the present invention to provide a method .of making thin steel armor l plate in which a full quench following heat treat- Y ment is utilized for developing high ballistic j properties. i 4 Y Likewise, it is an object of the present inven-V tion to provide a. method of making thin steel armor plate in which the plates are in certain instances treated prior to heat treatment so that Also it is an object of the present invention to provide an improved straightening step which v enables the removal of smallwrinkles.` kinks or buckles in a method of making thin steel armor plate, which such small wrinkles, kinks, or buckles making thin steelarmo'r- It is a further object or the present invention could not be removed or straightened in accordance with prior practice. e

Also it is an object of the present invention to provide a method of making steel armor plates incorporating some or all of 'the above objectives by `which armor plate of the thinner gauges, such as lA'f, 1/2", and up to l armor plate, may be manufactured having high ballistic properties.

Likewise, it is an object of the presentinvention to provide an improved steel armor plate product of the thinner gauges, of the order of up to l" in thickness, having an extremely uniform depth of case; having for 1A" plate for example, a Brinell hardness on the hard side of the order of from 500 to 550, and on the soft side of the order of from 400 to 445; having for 1A" plate e for example, a resistance to bullet penetration at striking velocities of the order of 2000 to 2100 feet per second; having for 1A plate a proportionately large resistance to impact; and having for heavier gauge armor plate up to l in thickness a comparable hardness and proportionately greater bullet penetration and impact resistances.

These and other objects may be obtained by the methods, procedures, steps, operations, and order ,and character thereof, hereinafter described in detail, and set forth in the appended claims, certain steps of which are diagrammatically shown in the drawings, in which:

Figure 1 is a plan view, with parts broken away, of two steel plates assembled for being carburized;

Fig. 2 is a side elevation of the plates shown in Fig. 1;

Fig. 3 is a diagrammatic sectional view of a carburizing box or pot with plates such as shown in Figs. 1 and 2 packed therein ready for carburization;

Fig. 4 is a view similar to Fig. 2, showing warpage which may occur during a certain stage of the carburization step;

Fig. 5 is an enlarged section taken on the line 5 5, Fig. 4;

Fig. 6 is an enlarged section taken on the line 6 8, Fig. 5;

Fig. 7 is an enlarged fragmentary sectional view of a plate which has been carburized and is ready for machining;

Fig. 8 is a view similar to Fig. 7, but showing the plate after machining, drilling and sizing;

Fig. 9 is a fragmentary diagrammatic view of a roughing straightening die illustrating the operation thereof;

Fig. 10 is a view similar to Fig. 9 of a finishing straightening die;

Fig. 11 is a side elevation of a completed armor plate ready for shipment;

Fig. 12 is a diagrammatic view of'a stand of rolls for imparting curvature to the armor plate during the processing thereof when desired;

Fig. 13 is a side elevation of an armor plate showing curvature imparted thereto by the rolls illustrated in Fig. 12;

Fig. 14 is a view similar to Fig. 13, but showing the plate after it has been heat treated and fully quenched; and

Fig. 15 is a view showing the plate of Fig-14 after it has been straightened.

Similar numerals refer to similar parts throughout the various figures of the drawings. The raw material for carrying out the improved method is ,alloy steel plates I6 as received from the steel mill of a type commonly used in the manufacture of armor plate, and

which may contain one or more of the following alloying metals: chromium, nickel, molybdenum, vanadium, manganese. For instance, steel plates made from S. A. E. steels such as Nos. 2515, 2520, 4815 or 4820 may be used. These plates are laid off and sheared or cut generally to size in ac'- cordance with specifications. No holes are drilled at this time.

The improved method thus initially departs from prior practice because, in accordance with prior practice, some or all of the holes, required by specifications, are at this time drilled so that two matched plates can be bolted together for carrying out the carburizing step. The elimination of hole drilling at-this time in accordance with the present invention, provides a number of advantages to be later referred to.

Next, a non-case or carbon resistant material commonly used in carburization, is sprayed on the side of a plate which is intended to be the soft side of a iinished plate. Here again, the procedure departs from prior practice, by spraying the non-case material instead of painting it. This results in a considerable saving in time and thereforein the cost of applying the non-case, even though more non-case material may be used. Moreover, the non-case spraying procedure enables the provision of a more uniform coating, or of a heavy non-case coating, if required, in a short time.

Two matched plates I6 are then temporarily clamped together with the non-case coated faces contacting. While thus temporarily clamped, the edges of the two plates are tack welded at a num- -ber of places around the periphery thereof as indicated at I1 in the drawings.

The securing vof a pair of plates together by tack welding rather than by bolting through drilled holes also provides a number of advantages to be later referred to.

Next,v the clamps are removed and the pairs of plates IGA, tack welded together, are packed in a .carburizing box or pot I8. In packing the plates IGA in the boxes I8, the plates are surrounded by carbonaceous material I9 of the usual character, which is high in carbon content and will liberate carbon to the plates at high temperatures.

The carburizing material, in accordance with usual practice, may be used over and over with the addition of some new material and the depth of the material I9 between plate layers when packed ordinarily ranges from 11/2 to 3 inches, depending upon the depth of case desired and the thickness of the plates.

In packing the plates- IBA in the boxes I8, all edges of all plates are kept away from the sides ofthe box and from touching each other, as illustrated,.so as to reduce as much as possible, any differential in the rate of heating and cooling of the plates and particularly the edges thereof during the carburizing step, which helps to control warpage and to facilitate machining at a later stage in the process.

Formerly, in packing the plates IGA in the boxes I8, the plate edge spacing from the box sides was not controlled, which resulted in variations in the plates due to a high differential in the rate of heating or cooling` thereof.

The box I8 is thenv covered with a lid 20 and sealed with iireclay 2| in the usual manner and placed in a carburizing furnace wherein the temperature is raised to from 1680 F. to 1700 F. furnace temperature in about four to six hours. The plates in the boxes I8 are thus treated at the t assasoe stated temperature inthe .atotalfurnaceontofurnaeeoiftimeofapproximately44to50hours,usuailyabout48hoursfor for yl pme. I. .A .Small variations in thefurnace time and temperaturearedeterminedbythe depthofcasedeyaired: the hardness ancedesiredzsteeianalysimandgrainsiseland wthesemitttersarekiiovrrnintlieart'otcariiuris-v deiremtheballiscredltingwherethesmallvariationsn'eordinsrilyleft larselyup'totheskiiloi the operator.

Ihesealedboxes il arethenremoved fromtbe furnaeeandaxepermittedtoslowly stone'cold. which may be from toiivetlarsorevenoneweek. i

practice ingwhichthe boxes were partially cooled in the fin-nace'andthen opened while stillwarm and the plates permitted tor cool in the'air. By using the cooling of the present in- -vention,;` the furnace capacity is ali Ithoughthe/elapsed time for the treatment yof any particular piece may be lengthened.v Also',

` I have discovered that the particular cooling procedure. after the treatment in the carburizing vfurnace renders a subsequent annealing operation, formerly required unnecessary. This annealing operation used to be requiredin accordance with prior practice in order to permit subsequent machining.v

Referring to the previously noted omission of .the initial hole drilling-step of the prior art, to

f3 warpogetenastoineressetneedseseaisewm thoplatesilotliatitlielpstoprevent,ratlierthan tooausainnersurfacecarburiaation. Asarenilt.pl'atessocarburisedhaveamuenmoreunif form depth or case on'the hard side and on-the edges ssindicated at ilCin thedrawlngs.

In Figs. 5 ando, the non-case material is y indicated at "D: and lama 3 smallpairedtestpiecesoi'platenmaybelocated W atvlriousregionsinthebox Il for subsequent testingas to depth and character of case. t

Afterthe boxes Il and contents thereof have cooled to be lstorie cold, the boxes are opened and the paired plates [IA are removed from the box. Next, the the welds the welds casesurface IlDgroimd oif. j

wnichare brittle and will preek; ons

kat this point in the procedure, en annealing step was required in accordance with prior practice. but is eliminated in accordance with the present invention. The plates at thistime are indicated at .IIE in Figure 'l` of the drawings.

The necessary holes are now drilled'in the plates IDE as indicated at 2l .in Fig.. 8, to meet specifications; also the plates are shaped to size by machining, and the edges may -be bevelled if required. as indicated at 23a, to produce thev plaies as shown at I IF. It is frequently unneces-v sary to remove the cased edges, but if the edges are bevelled, removal of the cased edges naturally results.

Ifit is desired or necessary thatfthe plates be bent to meet speciilcations, they may be bent at .thel carburizingystep, which preventsthe vi'naintenance of a' uniform softer inner or backing surr'face or region linthe plate; Likewise'rthebolts irequently'break 'duringthe carburizing step,

carburizationtocreepin f which obviously-.allows along the hole surfaces.

Moreover, if the bolt holes are too close to the edges of the plates, the plates may' crack between the holes andthe edges during carburlzation.

Alsorthe plate edges frequently warp open awayfrom one' another, permitting car-burization to creep-in along the' inner surface from the warped opened edges. and such warpage may alsooccur if'lany bolts break. These prior art -conditions have required considerable additional metal to be provided all around at the edges, in order that warped and inner surface carburized edges can be later removed and yet leave `a plate sized' in On the other hand. by welding it is assured y ,accordance'with specliication's.

this time and they may also be sheared for shap- As a `result of this procedure, -the amount of spoiled or cracked material is materially reduced .and necessary machining may be readily accomplished; Moreover, machining and drilling can be `niostaccurately done so as to insure amore accurateA location of drilled-holes and machined edgesfintheulthnate finished product. Likewise,

edgesand drilled holes are not carburlzed on the surfacesthereof. Accordingly, a "si'ioelr of carburized plates such vas indicated at `lillifin Flg."l, may be built up and drawn from )at this pointto'illl orders for plates of desired sizes and shapes, which materially facilitates the Aproduction thereof.

The steps of the method as thus farv described are used in making steel armor plate ofthe thinner gauges such asl/4", 1A", et" and upto 1f" that the plates will not break open orwarp open at thel edges. The welds positively hold the plates'together and,maintain a more intim-ate seal between the plate-edges. This seal, together with the imperiorate character of the putes during carburization, prevents inner surface carburization of the plates. l

Ii the plates warp during carburization, the

resulting connguration is as shown in a very exaggerated manner in Figsj-i, 5 and il, wherein each of the'plates il of the pair IGA will have an outward eonvexity as indicated at IBB. This 1| 'thin plate an'd may be used in the manufacture of even thicker armor plate. However, from this point on, the. procedure varies somewhat in "accordance with the thickness of the plates being made. 'I'he succeeding treatment in accordance with the present invention, of l/g" plate is, how-` ever, fundamentally the same as that usedin the thickness up to manufacture of plates ofv different 1" thick plate, as will be later described.'

Firstreferring to the` V plate procedure. the machined and drilled plates IGF, shown in Fig. 8, are placed in a heat treating furnace on a ilre brick hearth, in which furnace the temperature of the material is raised to' a point above `its A133 point (l375 F. to 1550 FJ. The plates are held at this temperature until the carbon in the case is fairly well in solution, which may 'be for approximately one hour. after which the plates are removed and quenched in oil maintained at a temperature of about to 120? F. until the plate temperature reaches the oil temperature. The temperature of the oil has two paired plates 'are separated by hitting are thereafter removed and the nonfactors, it controls the condition of the hard side of the plate, and it also controls warpage.

I have discovered that warm oil does better work than cold oil, for there is less tendency for the plates to warp or buckle with oil at 105 to 120 F. than with colder oil. A full quench at this stage of the process enables the high ballistic properties now being demanded in thin armor plate to be obtained, along with the desired hardness of case on the hard side. Atter quenching, the plates are placed in a tempering or drawing bath of oil maintained at about 400 F. for thirty minutes to one hour, and are then removed and cooled.

Thereafter, the usual hardness tests are made on the hard and soft sides, which may average for example, a Brlnell hardness on the hard side of 500 to 550, and on the soft side of 400 to 445.

The plates arethen straightened on a hammer o.' power press, which may include a set of roughing dies indicated somewhat diagrammatically in Fig. 9 at 24, and a set of finishing dies indicated somewhat diagrammatically in Fig. 10 at 25.

In the roughing die 24, a bottom die 26 is used, which has a very shallow concavity 21, `and a top die 28 which has a rounded nose 29. By locating the plates between the dies with any plate concavity'turned downward, and operating the pressI plates luntil the hard side is substantially convex as indicated at IBG in Fig. 13. The plates arel then permitted to cool with the soft side down on a cool iiat surface, which imparts a permanent set to the plates with the hard side convex, as shown in Fig. 13.

The plates IBG are then placed in a heat treating furnace on a i-lre brick hearth and raised to a temperature above the A03 point (1375 F. to 1550 F.) as in the 1A" plate procedure. The plates are held at this temperature until the carbon in the case is fairly well in solution, which may be for approximately one hour and a quarter, after which the plates are removed andl quenched in oil maintained at a. temperature of about 105 to 120 F. until the plate temperature reaches the oil temperature. As previously stated, the temperature of the oil has two factors, that of controlling the condition of the hard side and of warpage.

The usual hardness tests are made, which may, for 1/2" plates for example, average a Brlnell hardness on the hard side of 500 to 550, and on straightened on a hammer or power press, using either or both of the roughing dies 24 and iinstraightening operation without cracking or breaking the plates, the roughing die 24 is rst used and then the finishing die 25 is used. The finishing die has a similar bottom die 26 having a very shallow concavity 21, and a .top die 28A having a generally flat nose 29A rounded substantially on the same, or a slightly less radius, as that on which the bottom die concavity is formed.

The finishing die 25 also operates, as shown in' Fig. 10, upon material IGF with the concaved side down and the hard side up. However, the die surfaces 21 and 29A, due to their substantial width and substantially similar curvature, bottom on the material so that the die pressure is distributed along the entire surface of the wide nose of the top die, which may be an inch or more in width. This distributed pressure enables the small kinks or buckles or wrinkles to be pressed, squeezed or ironed out in such a manner that a ilat finished plate, such as indicated at 30 in Fig. 11, results. The plates 30 are then finally resized by grinding if necessary, inspected and shipped.

Now referring to the 1/2 plate procedure, the machined and drilled plates IGF, such as shown in Fig- 8, are normalized by a high temperature anneal, not suiiiciently long enough to spheroidize the carbon. This normalizing is accomplished by heating the plates for approximately one-half ishingdies 25, as previously described. Finally, the. plates 30a shown in Fig. l5, are resized by grinding if necessary, inspected and shipped.

Thus, the 1/2" plate procedure is fundamentally the same as the 1/4 plate procedure, except that the heat treating and quenching operations are preceded by a high temperature anneal and a rolling to place the plates in a condition ln which the hard side is substantially convex. The subsequent heat treating after rolling results in some shrinkage on the hard side, particularly during the full quench, which cannot be prevented. The convexity' imparted by the rolling operation is such that on shrinking during the full quench, the plates will not pass through a at condition to a concave shape on the hard side.

However, the inherent effect of the full quench in causing some shrinkage on the hard side, substantially reduces the convexity imparted by the rolling operation so that the amount of straightening necessary on the straightening dies is diminished.

Fig. 14 diagrammatically illustrates, in an exaggerated manner, the condition of the plates after the full quench in which the general convexity of the hard side is quite shallow, as indicated at 16H, and in which buckles, warps or kinks are indicated in an exaggerated manner at Thus, the high temperature anneal places the plates in the best condition for rolling. This rolling step must not be done while the plates are too hot, because the subsequent heat treatment will pull out the convexity imparted by rolling. Likewise, the rolling must not be done while the plates are too cold, or the material will crack while being rolled. The rolling of the plates, however, prior to heat treating, enables the platesto'be brought to the` straightening operation with the hard sideslightly convex and at the same time enables a full quench to be used in order to develop high ballistic properties.

This procedure of the present invention is a radical departure from prior practice, in which the plates were only given a partial quench, were then flattened or made slightly concave Aon the hard side and were then permitted to cool. dur-y the carburizing step.

accesos l ving which lcooling the plates reverse themselves from a `concave to .a slightly convex Vshape on t the -hard side; after which a straightening was f d performed.'l This prior practice procedure, however; in'nscessitating a partial quench followed "if-Infiniv miler straishteningoperation, prevented highest-ballistic properties from being developed t v, intheultimate product.

, The procedure in accordance with the vpresent Q -myentioa'for mam tmtksr pistes uur as it" plates'. up to l'.' plates is substantially the same as that for making 9." platos, excepting that the time for normalizing is proportionately longer nace is proportionately longer depending upon the thickness of the plates.

The resulting finished platesA have a hardness comparable to plates made in accordance with prior practice, but have ballistic resistances from 10 to 15 per cent higher than in any plates made in accordance with prior practice; and the resulting plates also have a much greater impact resistance.

l'br example, V4" armor plate made in accordance with the present process, under actual tests; resists bullet penetration by standard 1 armor penetration bullets at striking velocities .up to 200() to 2100 feet per second.

Referring to the carburizing step, right and left plates are usually required,vso that a matching or pairing of plates IBA can ordinarily be yeected. However, if only one plate is required, or if a matching of plates is not practical, a dummy plate can be welded to the plate made in accordance with specifications,

In its broadest aspects, the invention which Y Vcomprises the present improved method contemplates an entire realignment of steps,.and radical changesv in and omissions of steps, used in the manufacturev of armor plate of the thinnerv gauges, which materially simplifies the manufacture of auch armor plate and renders it possible to make armor plate satisfying present day' requirements.

Thus, the present invention provides for overcoming the difficulties and eliminating many of` the v operations and consequent disadvantages resulting, involved in the prior practice of makd ing armor plate of the thinner gauges.

In the foregoing description, certain terms have been used for brevity, clearness and understanding, but no unnecessary limitations are to -be implied therefrom .beyond the requirements of the prior art; because such wordsare utilized for descriptive purposes hereingand not for the purgp'ose ofrlimitation, and areintended to be broadly -con`strued.-

, I .L a Moreover, the invention is `not limited to they production of thev exact structures shown herein,

because armor plate" offsulstantially any thickness in the thinner gauges, up to 1" in thickness may be made in accordance with the described `method without departing from the 'scope of the j present' invention, l

Likewise,fcertaln of therste'ps, such as the carburizing steps, thepreparation of the plates after `carburizing and before heat treatment, the

preparation of the vplates for heat treatment, and

" the' straightening thereof after heat treatment, Y may be advantageously used in the manufacture of. armor plate thicker vthan l in thickness, without departingl fromV the scope of the present invention. d

in carrying out Having /now described the features of the invention, the preferred steps and preferred sequence of steps used in carying out the improved method, the advantages and results cb- -tainedby the useof the same, and the improved resulting armor IpIaieprOduct; the new and usefui methods, method steps, operations, and products, and reasonable mechanical equivalents f thereof obvious to those skilled in the art, are set depending'upon the thickness of the plates, and the time of treatment in the heat treating furforth in the appended claims.

I claim: l

l. In the manufacture of steel armor plate of the thinner gauges of the order `of up to 1" in thickness having a hard case side and a softer backing side, the steps of coating the backing side of van imperiorate plate with a non-case material,` covering the coated side with another l imperforate plate. tack-welding the edges of said plates together, carburizin'g the plates, and then removing' the weids' and non-case material and drilling and machining the plates.

2.v In the manufacture of steel armor plate of the thinner gauges of the order of up to 1I in thickness `having a hard case side and a. softer backing, side, the steps of coating the backing side of plates with a non-case material, carburizing the plates in pairs with the non-case coated surfaces of the plates of each pair facing each other, maintaining the extreme contacting surfaces adjacent the edges of the plates of each pair in'intimate contact during carburization, then drillingv the plates, and then heat treating and straightening the plates.

. y3.l In the manufacture of steel armor plate of the-thinner gauges of the order of up to 1" in thickness having a hard case side and a softer backing]side,"the steps of carburizing the case side .of imperforate plates, holding the plates atthe edges lsothat only convex plate warpage on the hard side' can occur during carburization, then drilling the plates,tand then heat treating and straightening the plates.

4. In the manufacture of steel armor plate of vthe thinner gauges of the order of up to 1" in thickness having a hard case side and a softer `backing side,- the steps of carburizing the case sides vof plates in a box in the presence of a carbonaceous material by the application of heat,

-maintaining a 'substantial thickness of carbonac'eous material between the box walls and all plate edges and surfaces to control diiferentials in the rate of heating -and cooling and resultant wai-page of the plates throughout during carburization, then slowly cooling the plates,` then after cooling drilling the plates without annealing the plates, and then heat treating and'straightening the plates.

, 5. In themanufacture of steel varmor plateof the thinner gauges of the orderof upto .1," in thickness having a hard case side and a softer backing side, the steps of carburizing the case sides of imperforate plates in a sealed box in backing-side,` steps of carburizing the case sides cir imperforateplate blanks in pairs in a sealed box in the Apresence ofa carbonaceous material by heating the sealed box in a furnace, slowly cooling the paired plate Ablanks in the sealed box until stone cold; then after cooling, shearing, drilling, and machining'the blanks to form plates of specified shape from said plate blank without annealing the blanks; and then heat treating and straightening the plates.

'7. In the manufacture of steel armor plate of taining a substantial thickness of carbonaceous material between the box walls and all plate edges and surfaces to control differentials in the rate of heating and cooling and resultant warpage of the plates throughout during heating and cooling, then removing the welds and non-case material and drilling and machining the plates, and then heat treating and straightening the plates.

8. In the manufacture of steel armor plate of l the thinner gauges of the order of up to 1 in thickness having a hard case side and a softer backing side, the steps of spraying a non-case material on the backing side of imperforate plates, covering the backing side of one plate with another to form a pair, tack welding the edges of said plates together to hold and maintain the extreme contacting surfaces adjacent the edges of the plates of each pair in intimate contact so that only convex plate warpage on the hard side can occur during subsequent carburization, carburizing the plates in a sealed box in the presence of a carbonaceous material by heating the sealed box in a furnace, slowly cooling the plates in the sealed box until stone cold, maintaining a substantial thickness of carbonaceous material between the box walls and all plate edges and surfaces to control differentials in the rate of heating and cooling and resultant warpage of the plates throughout during heating and cooling, then removing the welds and non-case material and drilling and machining the plates, and then heat treating and straightening the plates.

9. In the manufacture of steel armor plate of the thinner gauges of the order of up to 1 in thickness having a hard case side and a softer backing side, the steps of spraying a non-case material on the backing side of imperforate plates; temporarily clamping two plates together with the non-case covered sides contacting to form a pair; tack welding the edges of said paired plates together to hold and maintain the extreme contacting surfaces adjacent the edges of the plates of each pair in intimate contact so that only convex plate warpage on the hard side can occur during subsequent carburization; removing the clamps; packing tack welded paired plates in a box in carbonaceous material with a substantial thickness of carbonaceous material between the box walls and all plate edges and surfaces to control differentials in the rate of heating and cooling and resultant warpage of the plates throughout during subsequent heating and cooling; sealing the box; heating the sealed box in a furnace to treat the plates for from about forty-four to ilfty hours at about 1680 to 1700" F.; removing the sealed box from the furnace and slowly cooling the plates in the sealed box for from four clays to-one week until stone cold; removing the paired plates from the box; removing the welds and non-case material from the plates; drilling and machining the plates to specified shape; and then heat treating and straightening the plates.

10. In the manufacture of steel armor plate of the thinner gauges ofthe order-'up to l" in thickness having a hard case side and a softer backing side, the steps of carburizing the case side of a plate, then heat treating the plate in a heat treating furnace until the carbon in the case side is fairly well in solution, then fully quenching the plate in oil to an oil temperature of about'105 to 120 F., and then straightening the plate.

1l. In the manufacture of steel armor plate less than 1/2"y thick having a hard case side l and a softer backing side, the steps of carburizing the case side of a plate, then heat treati-ng the plate in a heat treating furnace until the carbon in the case side isffairly well in solution, then fully quenching the plate in oil to an oil temperature of about F. to 120 F., then tempering the plate, and then straightening the plate.

12. In the manufacture of steel armor plate of the thinner gauges of the order of up to -1" in thickness having a hard case side and a softer backing side, the steps of carburizing the Vcase side of a plate, then heat treating the plate in a heat treating furnace for one hour or more at about 1375 to 1550 F. until the carbon in the case side is fairly Well in solution, then fully quenching the plate in oil to an oil temperature of about 105 to 120 F., and then straightening the plate.

13. In the manufacture of steel armor plate of the thinner gauges of the order of up to 1" in thickness having a hard case side and a softer backing side, the steps of carburizing the case side of a plate, then heating the plate, then fully quenching the plate in oil to an oil temperature of about 105 F. to 120 F., and then straightening the plate by a multiplicity of blows between dies having slightly curved work contacting faces of substantial width and length exerting a distributed squeezing pressure on the work.

14. In the manufacture of steel armor plate of the thinner gauges of the order of up'to 1" in thickness having a hard case side and a softer backing side, the steps of carburizing the case side of a plate, then heating the plate, then fully quenching the plate in oilto an oil temperature of about 105 F. to 120 F., then removing major warpage resulting from quenching by subjecting the' plate` to a multiplicity of blows.

between dies having curved work contacting faces of substantially different curvature, and then removing smaller kinks and Wrinkles by subjecting the plate to -a multiplicity of blows between dies having slightly curved work contacting faces of substantially the same curvature and of substantial width and length exerting a distributed squeezing pressure on the work.

15. In the manufacture of steel armor plate of the thinner gauges of the order of up to 1" in thickness having a hard case side and a softer backing side, the steps of carburizing the case side of a plate, then normalizing the plate by a high temperature anneal, then cooling the plate side of a plate, then heating thc plate' and h to normalize the plate. then cooling the plate f air toapproximately 600 1?., than rolling .the plate until the case side is convex,then heating 'thelng it at about 1700 E101' up to about one.

plate until the carbon in the case side is`A fairly.

suur.-

wen in so1uuou, then fuiiy quencmngtus plate y in ou to an ou temperance of about 105 tu 120 F., and then straightening the plate.

17. In the manufacture of steel armor plate" high temperature anneal, then while the plate.

12.024.808 7 'I lin having a hard case' side and a softer theplate until the case side is convex, then heatside. .the/steps of carburizing the case 'inl the plate in a heat treating fiunace for ap proximately one and one-half to two jat' about 137s .to 1500 r. until the csrbon'in case side`is fairly well in ulution."th cnhm!;. plate in oil to of about 105 to 120 F., and their theplate. .l L.

22. In the manufacture of steel armor plate of the thinner gauges of the' order of up to 1" in thickness having s. hard case side and asofter backing side, the steps of spraying a non-cale still retains a substantial portion of the annealing heat rolling the plate untill the case side has such convexity that shrinkage of the case produce concavity in the case side, then heating the plate, then fully quenching then straightening the plate.

18. In the manufacture of steel armor plate of the thinner gauges of the order of l'.' to 1" i in thickness having a hard case side and a softer backing side, the steps of carburizing the case side x of a plate, then normalizing the plate by a high temperature anneal, then air cooling the plate to 'about 600 F., -then rolling the'plate 'lo impart convexity `to the case side thereof, then heat yso side during a subsequent full quench will not material on the backing side o f an imperforate plate, covering the backingv side with another im-- perforate plate, tack welding the edges of said plates together, carburizing the plates, removing the welds and non-case material, drilling and machining the plates, heat treating the plates in a heat treating furnace until the carbon in the case side is fairly well in solution, then fully quenching the plates in oil to an oil temperature of about 105 to 120 F., and then straightening the plates.

the plate. and

treating the plate in a heat treating furnace for one hour or moreat about 1375to 1550 l". until the carbon in the case ls fairly well in solution, then fully quenching the plate in oil to an 1 oil'temperature of about 105 to 120 F., and then- :i straightening the plate.

19. In the manufacture of steel armor plate less than thick having a hard case side and a softer backing side. the steps of carburizing the case side of a plate, then heating the plate in a heat treating furnace for approximately one to one and one-quarter hours at about 13'15" to 1550 F. until thecai-.bon in the case\side is fairly well in solution. then' fullyrquenching the plate in oil to an oil temperature of about 105. to' 120 F., then tempering the plate in an oil `bsth at about 400 F. for from 'one-naif to one hour, then cooling the plate, and then straightenq ingtheplate.

20. In the manufacture vof steel armor plate from about V2" to less than thick having a hard case side and a softer backing side, the steps .of carburizing the case side of a plate. then heating the plate and soaking it at about 1700" F. for from about thirty to about forty minutes to normalize the plate.' then cooling the plate in air to approximately 800'.1l., than.` rolling the plate until the case side is convex, then heating the plate in a heat `treating furnace for approximately one and one-quarter to one and one-half hours at about 1375 to 1550` I". until the carbon in the case side is fairly well in solution, then fully quenching the plate in oil to an loil temperature of about 105 to 120 F., and then o straightening the plate.

21. In' the manufacture of steel armor plate.

from about %""to less than 1" thick having a hard case side and a softer backing side. the

i steps of carburizing the case side of the plate. then heating the plate and soaking it at about 1700" F. for fromabout forty to about sixty 23. In the manufacture of steel armor plate of the thinner gauges of the order of up to l"v in thickness having ahard case side and a softer backing side, the steps of spraying a non-case materiall on the backing side lof an imperforate plate. covering the backing side with another imperforate plate, tack welding the edges4 of said' plates together, carburizing the plates, removing the weids and non-case material, drilling and machining the plates, normalizing the plates by a high temperature anneal, .then cooling the plates in air to approximately 600 F., then rolling the plates until the case side is convex,- then heating 'the plates, vthen fully quenching the plates,.and `then straightening the plates. f

24. `In the manufacture of'steei Varmor plate thick having a hard caseside and a. softer 'backing-side, `the steps of coating the backing side of ci' said plates together. carburizing theplates in a sealed of carbonaceous material between the box'walls ching the plates.-

at all plate edges and surfaces' to control dif-A Y ferentials in the rate of heating and cooling andV resultant warpage of the plates throughout during heating and cooling,

F., then tempering the plates, and then straight- 25.` In the manufacture of a sealed box in the presence of a carbonaceous material by heating the sealed an imperforate piatewlthla non` I f case material, covering the coated side-with-am g I' other imperforate plate, tack welding Ythe. edges box in the .presence oi' a carbonaceous .material by heating the sealed box 'in-a furnace.

unta...

removing the welds and non` i oase material, drilling and machining the plates, then heat treating the plateain a heat treating f i furnace-'until the carbon in the case side is fairly v weilinsolution, then fully quenching the plates in oil to an oil temperature of about to 120."

steel `armor plate of the thinner' gauges ofthe order of up to 1"v in thickness having a hard case, 'sideand a.A softer backingside, the steps of coating the backf ing side of an imperforate plate with a non# case material, covering the coated side with an-L' other imperforate plate, tack-welding theedges: of said plates together, carburizing the plates in box in a furnace, slowlycoolingthe plates in the sealed box until stone cold, maintaining a substantial of carbonaceous material between the box walls at al1 plate edges and surfaces to controldife'. ferentials in the rate of'heating and cooling and resultant warpage of the plates throughout during heating and cooling, removing the welds and non-case material, drilling and machining the plates, then normalizing the plates by-a high temperature anneal, then while the plates still retain a substantial portion of the annealing heat rolling the plates until the case side has such ,convexity that shrinkage of the case side dur- 'after cooling forming holes through the carburized part of the plate and machining the plate to specified shape without annealing the plate, and then heat treating and straightening the plate.

27. In the manufacture of steel armor plate of the thinner gauges of the order of up to 1" in thickness having a hard case side and a softer backing side, the steps of spraying a non-case material on the backing side of a plate, carburizing the case side of the plate and slowly fooling the plate; then after cooling removing the non-case material, forming holes through the carburized part of the plate, and machining the plate to specified shape all without annealing the plate; and then heat treatingand straightening n the plate.

ALBERT L. ABBOTT. 

